1. Field of the Invention
The present invention relates to an electronic apparatus that is driven by electric power of a generator in which a voltage of generated power changes as time elapses or a power supply in which the voltage thereof changes as time elapses, particularly to a portable electronic apparatus.
2. Description of the Related Art
Conventional electric apparatuses include a generator in which the voltage of generated power changes as time elapses or a power supply in which the voltage thereof changes as time elapses. In such electronic apparatuses, in order to continuously operate a driving circuit of the electronic apparatuses, a power supply capacity of the generator or the power supply is set so that the voltage of the generator or the power supply does not fall below the minimum driving voltage of the driving circuit of the electronic apparatuses even if the voltage changes as time elapses.
Also, as shown in FIG. 9, conventional electronic apparatuses include a generator in which the voltage of the generated power changes as time elapses or a power supply 90 in which the voltage changes as time elapses, a booster circuit 92 for boosting such generated power or the power of the power supply, and an oscillator circuit 91 that drives the booster circuit 92. In the electronic apparatus, the oscillator circuit 91 is driven by the generator in which the voltage of the generated power changes as time elapses or the power supply 90 in which the voltage changes as time elapses. Further, the booster circuit 92 is driven by an output clock of the oscillator circuit 91, and the power of the generator or the power supply 90 in which the voltage of the supplied power changes as time elapses is boosted by the booster circuit 92, to thereby drive a driving circuit of the electronic apparatus. Accordingly, in order to continuously operate the driving circuit of the electronic apparatus, a power supply capacity of the generator or the power supply 90 is set so that the voltage of the generator or the power supply 90 does not fall below the minimum driving voltage of the oscillator circuit 91 even if the voltage changes as time elapses.
Also, conventional electronic apparatuses include a generator in which the voltage of the generated power changes as time elapses or a power supply in which the voltage changes as time elapses, a booster circuit for boosting such generated power or the power of the power supply, an oscillator circuit that drives the booster circuit, and a capacitor for accumulating the boosted power and supplying power to a driving circuit of the electronic apparatus. In this electronic apparatus, the oscillator circuit is driven using the power accumulated in the capacitor, the booster circuit is driven by an output clock of the oscillator circuit, and the power of the generator or the power supply in which the voltage of supplied power changes as time elapses is boosted by the booster circuit. Then, the booster power is accumulated in the capacitor so that the driving circuit of the electronic apparatus is driven by the power of the capacitor. Accordingly, in order to continuously operate the driving circuit of the electronic apparatus, the capacitor is always charged so that the power accumulated in the capacitor does not become empty and that the voltage of the capacitor does not fall below the minimum driving voltage of the oscillator circuit.
Now, an example of an electronic apparatus using a thermoelectric conversion device as a generator is shown as a prior art. In the thermoelectric conversion device, a P-type thermoelectric material element and an N-type thermoelectric material element are sandwiched between two substrates, an a plurality of P-type thermoelectric material elements and N-type thermoelectric material elements form a p-n junction on the substrates through an electrically conductive material such as metal to be connected in series with one another. The thermoelectric conversion device produces electromotive power by a temperature difference between the two substrates, to thereby generate power. The power generated per thermoelectric material element is about 200 .mu.V/.degree.C. When, for example, a circuit that drives at 1.5 V is directly driven by the thermoelectric conversion device, assuming that the temperature difference between the substrates is 2.degree.C., at least 1,875 pairs of p-n junctions are required. Furthermore, since the thermoelectric conversion device is influenced by the atmospheric temperature, a large margin for generating power is allowed to thereby increase pairs of p-n junctions. Accordingly, the electronic apparatus using the thermoelectric conversion device requires a large heat radiating plate, because the size of the thermoelectric conversion device is increased and the number of heat-propagating paths is also increased.
FIG. 30 shows a conventional booster circuit. In FIG. 30, reference numeral 470 denotes an electromotive voltage input terminal for inputting the electromotive voltage Vp of the power supply 90, 471 denotes a first clock signal input terminal for inputting a first clock signal P11 which is one of clock signals P1 outputted from the oscillator circuit 91, 472 denotes a second clock signal input terminal for inputting a second clock signal P12 which is one of the clock signals P1, 473 denotes a boosted voltage output terminal for outputting a boosted voltage Vdd, 474 denotes a booster unit, and 483 denotes a diode.
The more the number of booster units 474 connected in series with one another is, the more the boosting factor is. In the booster unit 474, reference numeral 479 denotes an input terminal, 480 denotes a boosted voltage output terminal, 481 denotes a first clock signal input terminal for inputting a first clock signal P11, 482 denotes a second clock signal input terminal for inputting a second clock signal P12, 475 and 476 denote diodes, and 477 and 478 denote capacitors.
A signal obtained by inverting the first clock signal P1 is a second clock signal P2. Since operation of the circuit is already well known, it is omitted.
In the conventional electronic apparatuses, in order to continuously operate a driving circuit of the electronic apparatus, a power supply capacity of a generator or a power supply is set so that the voltage of the generator or the power supply does not fall below the minimum driving voltage of the driving circuit of the electronic apparatus even if the voltage changes as time elapses. For this reason, when the voltage of the generator or the power supply exceeds the minimum driving voltage of the driving circuit of the electronic apparatus, the electric power is wastefully used, whereby the efficiency of the whole system is deteriorated. Furthermore, since the power supply capacity is set so that the voltage of the generator or the power supply does not fall below the minimum driving voltage of the driving circuit of the electronic apparatus, the generator or the power supply is unpreferably enlarged. Particularly, in the case where the above-described electronic apparatus is used in a portable apparatus, there is such a problem that the size of the generator or the power supply is increased.
Furthermore, in the conventional electronic apparatus, an oscillator circuit is driven by the power of the generator or the power supply, and a booster circuit is driven by a clock signal from the oscillator circuit. For this reason, even if the voltage of the generator or the power supply falls slightly below the minimum driving voltage of the oscillator circuit, the oscillator circuit, the booster circuit, and then the whole system stop their operations. At this time, the generator or the power supply supplies, to the booster circuit, electric power whose voltage is only slightly below the voltage of the minimum driving voltage of the oscillator circuit. Since the system is, however, in a non-operation state, the efficiency of the whole system is considerably deteriorated. Therefore, in order to continuously supply power to the driving circuit of the electronic apparatus, it is required that the voltage of the generator or the power supply does not fall below the minimum driving voltage of the oscillator circuit even if the voltage changes as time elapses. On the other hand, in the case where the voltage of the generator or the power supply greatly exceeds the minimum driving voltage of the oscillator circuit, the voltage after boosting operation greatly exceeds a voltage necessary for the driving circuit of the electronic apparatus. The thus generated excess power is changed into useless energy such as heat. Furthermore, since the power supply capacity is set so that the voltage of the generator or the power supply does not fall below the minimum driving voltage of the oscillator circuit, there is such a problem that the size of generator or the power supply is unpreferably increased.
Also, in the conventional electronic apparatus, power accumulated in the capacitor is used to drive the oscillator circuit and boost the output power of the generator or the power supply. The thus boosted power is accumulated in the capacitor to drive the driving circuit of the electronic apparatus by the power of the capacitor. Accordingly, in order to continuously operate the driving circuit of the electronic apparatus, the capacitor is always charges so that the power of the capacitor does not become empty and the voltage of the capacitor does not fall below the minimum driving voltage of the oscillator circuit. Therefore, since the power of the capacitor becomes empty if the charged power of the capacitor is less than the power that is consumed by the driving circuit of the electronic apparatus, the generator or the power supply requires large power supply capacity. Also, there is such a problem that when the voltage of the capacitor falls below the minimum driving voltage of the oscillator circuit, the operation of the whole system is stopped.
In the case where the thermoelectric conversion device is used as the generator of the above-described electronic apparatus, thermoelectric material elements must be connected in series with one another so that the output voltage of the thermoelectric conversion device always exceeds the minimum diving voltage of the driving circuit or oscillator circuit of the electronic apparatus. Further, since the thermoelectric conversion device generates power by a temperature difference and is influenced by the atmospheric temperature, a larger number of the thermoelectric material element are required to be connected in series with one another. For this reason, the thermoelectric conversion device is enlarged, and the number of heat-propagating paths is increased, so that a larger heat radiating plate is required. Accordingly, it is difficult to employ the above-described electronic apparatus for a portable apparatus.
The conventional voltage booster system has first a disadvantage that its booster circuit needs to have a plurality of diodes and has a loss caused by the diodes. A Schottky diode is often used as the diode in order to reduce a forward voltage drop. However, even using the Schottky diode cannot avoid a voltage loss and power loss caused by a forward voltage loss, and there is a problem that a voltage of 0.2 V or so is lost in each of the Schottky diodes.
Next, since the conventional booster circuit does not have a means for detecting the voltage of a power supply, it cannot set the boosting factor of the booster circuit at an appropriate value according to the voltage of the power supply. Namely, there are problems that a charging efficiency is dropped by a fact that when a secondary battery is charged by a certain boosted voltage of the booster system, the trouble of charging a secondary battery through a booster circuit having a high boosting factor which is great in loss is taken even in case that the secondary battery can be charged by a booster circuit having a low boosting factor thanks to a sufficiently high voltage of the power supply, and that a boosted voltage exceeds the upper limit of a driving voltage for driving an IC or the like since the voltage of a power supply becomes higher in case that the IC or the like is driven by the boosted voltage.